Source file src/pkg/runtime/error.go

     1	// Copyright 2010 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package runtime
     6	
     7	// The Error interface identifies a run time error.
     8	type Error interface {
     9		String() string
    10	
    11		// RuntimeError is a no-op function but
    12		// serves to distinguish types that are runtime
    13		// errors from ordinary os.Errors: a type is a
    14		// runtime error if it has a RuntimeError method.
    15		RuntimeError()
    16	}
    17	
    18	// A TypeAssertionError explains a failed type assertion.
    19	type TypeAssertionError struct {
    20		interfaceType   Type // interface had this type
    21		concreteType    Type // concrete value had this type
    22		assertedType    Type // asserted type
    23		interfaceString string
    24		concreteString  string
    25		assertedString  string
    26		missingMethod   string // one method needed by Interface, missing from Concrete
    27	}
    28	
    29	func (*TypeAssertionError) RuntimeError() {}
    30	
    31	func (e *TypeAssertionError) String() string {
    32		inter := e.interfaceString
    33		if inter == "" {
    34			inter = "interface"
    35		}
    36		if e.concreteType == nil {
    37			return "interface conversion: " + inter + " is nil, not " + e.assertedString
    38		}
    39		if e.missingMethod == "" {
    40			return "interface conversion: " + inter + " is " + e.concreteString +
    41				", not " + e.assertedString
    42		}
    43		return "interface conversion: " + e.concreteString + " is not " + e.assertedString +
    44			": missing method " + e.missingMethod
    45	}
    46	
    47	// Concrete returns the type of the concrete value in the failed type assertion.
    48	// If the interface value was nil, Concrete returns nil.
    49	func (e *TypeAssertionError) Concrete() Type {
    50		return e.concreteType
    51	}
    52	
    53	// Asserted returns the type incorrectly asserted by the type assertion.
    54	func (e *TypeAssertionError) Asserted() Type {
    55		return e.assertedType
    56	}
    57	
    58	// If the type assertion is to an interface type, MissingMethod returns the
    59	// name of a method needed to satisfy that interface type but not implemented
    60	// by Concrete.  If there are multiple such methods,
    61	// MissingMethod returns one; which one is unspecified.
    62	// If the type assertion is not to an interface type, MissingMethod returns an empty string.
    63	func (e *TypeAssertionError) MissingMethod() string {
    64		return e.missingMethod
    65	}
    66	
    67	// For calling from C.
    68	func newTypeAssertionError(pt1, pt2, pt3 *Type, ps1, ps2, ps3 *string, pmeth *string, ret *interface{}) {
    69		var t1, t2, t3 Type
    70		var s1, s2, s3, meth string
    71	
    72		if pt1 != nil {
    73			t1 = *pt1
    74		}
    75		if pt2 != nil {
    76			t2 = *pt2
    77		}
    78		if pt3 != nil {
    79			t3 = *pt3
    80		}
    81		if ps1 != nil {
    82			s1 = *ps1
    83		}
    84		if ps2 != nil {
    85			s2 = *ps2
    86		}
    87		if ps3 != nil {
    88			s3 = *ps3
    89		}
    90		if pmeth != nil {
    91			meth = *pmeth
    92		}
    93		*ret = &TypeAssertionError{t1, t2, t3, s1, s2, s3, meth}
    94	}
    95	
    96	// An errorString represents a runtime error described by a single string.
    97	type errorString string
    98	
    99	func (e errorString) RuntimeError() {}
   100	
   101	func (e errorString) String() string {
   102		return "runtime error: " + string(e)
   103	}
   104	
   105	// For calling from C.
   106	func newErrorString(s string, ret *interface{}) {
   107		*ret = errorString(s)
   108	}
   109	
   110	type stringer interface {
   111		String() string
   112	}
   113	
   114	func typestring(interface{}) string
   115	
   116	// For calling from C.
   117	// Prints an argument passed to panic.
   118	// There's room for arbitrary complexity here, but we keep it
   119	// simple and handle just a few important cases: int, string, and Stringer.
   120	func printany(i interface{}) {
   121		switch v := i.(type) {
   122		case nil:
   123			print("nil")
   124		case stringer:
   125			print(v.String())
   126		case int:
   127			print(v)
   128		case string:
   129			print(v)
   130		default:
   131			print("(", typestring(i), ") ", i)
   132		}
   133	}
   134	
   135	// called from generated code
   136	func panicwrap(pkg, typ, meth string) {
   137		panic("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer")
   138	}
The Go Programming Language

Source file src/pkg/runtime/error.go
